1. Field of the invention
The present invention is concerned with an apparatus for exposure of both sides of printed circuit boards by means of a contact print comprising a master copy and printed circuit plate holder guided in parallel between two light sources in a mounting rack provided with feeding members and disposed with respectively one portion above and one portion below the exposure plane.
2. Description of the Prior Art
To produce the current paths of an electronic circuit on printed circuit plates, it is well known in the art to provide the printed circuit plates with light sensitive coatings and to transfer the circuit diagram concerned by means of master copies applied and by exposure, to the said coating. As regards exposure, this is performed in different ways, viz. by combining the printed circuit boards respectively to be exposed with the two master copies and transparent masks to form a package allowing the said package to pass through a suitable exposure implement, or by first exposing the one side of the printed circuit plate along with the appertaining master copy on a suitable copying device and subsequently replacing the printed circuit plate with the master copy for the other side to the second exposure device next thereto. This will, of course, require the master copies to be located in precisely positioned association to the printed circuit board which is achieved by way of suitable fitting members. According to the former method, each printed circuit board to be exposed will have to be equipped with the master copies and transported in the form of a package through the exposing device; this envolves, of course, the disadvantage that, in this manner, one cannot simply continuously transport only the printed circuit boards of a whole series of identical circuit diagram through the exposing equipment but rather respectively only the package completely prepared for each printed circuit plate necessitating availability of a plurality of master copies of an identical circuit diagram if an at least approximately continuous way of operation is to be safeguarded. Such a continuous way of operation, admittedly, is safeguarded by the latter method. However, this is at the expense of relatively extensive mechanical efforts envolving two exposing systems and the required replacement mechanical means for the printed circuit boards.